Recording/reproducing apparatus having a substituting part substituting for burst errors and a method of substituting for burst errors

ABSTRACT

A recording/reproducing apparatus records and reproduces, over a partial response channel, a recording signal produced by encoding data according to a convolutional code and reproduces the data from a reproduction signal by iterative decoding using likelihood information. A burst error detector detects a burst error part in the reproduction signal. A substituting part substitutes, for a sampling value included in the burst error part, a predetermined value according to a detected result of the burst error detector.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to datarecording/reproducing apparatuses, and more particularly, to a datarecording/reproducing apparatus having a substituting part substitutingfor a burst error and to a method of substituting for a burst error.

[0003] 2. Description of the Related Art

[0004] Apparatuses that record and reproduce data include variousrecording/reproducing apparatuses, such as recording/reproducingapparatuses of magnetic disks, magnetic tapes, optical disks, magneticoptical disks, and the like. In order to record data on such media,magnetic recording marks are mainly used. It is possible to save datapermanently and at lower cost than semiconductor memories by magneticrecording. Nowadays, recording/reproducing apparatuses are essential asinformation recording apparatuses for computers, for recording such asimages and image information having a lot of information.

[0005]FIG. 1 shows the construction of a conventional data recordingapparatus.

[0006] First, a description will be given of a case where data arerecorded. User data U_(k) are input to an encoder 101 that modulates theuser data U_(k) to codes that can be iteratively decoded. Then, datainterleaved via a puncture part (MUX puncture) 102 and an interleaver(π) 103 are supplied to an LD driver 104. The LD driver 104 modulates alaser beam based on the supplied data and records the data on aninformation recording medium 105. In an example shown in FIG. 1, amagnetic optical disk is used as the information recording medium 105(hereinafter referred to as the “magnetic optical disk 105”). However, amagnetic disk, an optical disk, and other information recording mediamay also be used. In the case of a magnetic disk, the data are suppliedto a magnetic head suitable for the recording medium.

[0007] Next, a description will be given of a case where data arereproduced from the magnetic optical disk 105. Recording marks arereproduced from the magnetic optical disk 105 by a head and a MOreproduction signal is obtained. A recording/reproducing system 106constructed by a writing head, the magnetic optical disk 105, and thereproducing head forms a partial response channel (PR channel) havingcharacteristics such as PR (1, 1). The reproduced MO reproduction signalis amplified by an amplifier 110. Then, the amplitude of the signal iscontrolled by an AGC 111, and thereafter waveform equalization isperformed on the signal by a low-pass filter (LPF) 112 and an equalizer(EQ) 113. The MO reproduction signal Yi subjected to waveformequalization as described above is converted to a digital signal by anA/D converter 114 by using a clock synchronized with the reproductionsignal. Then, the digital signal thus converted is accumulated in amemory 115.

[0008] Next, based on the data accumulated in the memory 115, the userdata are reproduced by a iterative decoder 116 such as a turbo decoder.The iterative decoder 116 is controlled by a controller 117 (forexample, an ODC in the case of a magnetic optical disk apparatus). Theiterative decoder 116 decodes the user data through iterative decodingof the number of times determined by the controller 117.

[0009]FIG. 2 shows an example of the encoder 101 that encodes the userdata into codes for performing iterative decoding. The encoder shown inFIG. 2 is an iterative convolutional encoder and is constructed byregisters 201 and 202, and exclusive ORs 203 and 204. The encoder shownin FIG. 2 generates a parity sequence p_(k) from the user data sequenceU_(k).

[0010]FIG. 3 shows an example of a conventional construction of theiterative decoder 116 in FIG. 1. Data (a reception signal sequence)y_(i) represent a reception signal digitized by the A/D converter 114and accumulated in the memory 115 shown in FIG. 1. The sampling datay_(i) are supplied to an a posteriori probability decoder (PR ChannelAPP) 301. The a posteriori probability decoder 301 calculates, under thecondition where input sampling value Y (y₁, y₂, y₃, . . . y_(n)) isdetected, a logarithmic likelihood ratio L(c_(i)*) between theprobability P (ci=1|y) that the next input bit ci is 1 and theprobability P (ci=0|y) that ci is 0. When iteration is made for thefirst time, a priori information La(c_(i)) input to the a posterioriprobability decoder 301 is all zeros. This represents that theprobability that all of the bits ci are “1” and the probability that allof the bits ci are “0” are the same probability (are equal).

[0011] Then, the a priori information La(c_(i)) is subtracted fromL(c_(i)*), which is the output of the a posteriori probability decoder301, by a subtractor 302 so as to obtain extrinsic likelihoodinformation Le(c). The extrinsic likelihood information Le(c) isconverted by a deinterleaver 303 and thereafter sent to a depuncturepart 304. The depuncture part 304 converts the deinterleaved extrinsiclikelihood information Le(c) to likelihood information L(u_(k))corresponding to a data bit U_(k) and likelihood information L(P_(k))corresponding to a parity bit P_(k) and supplies the information to acode decoder (Code APP) 305. The code decoder 305 outputs a logarithmiclikelihood ratio L(u*) with respect to the data bit u_(k) and alogarithmic likelihood ratio L(p*) with respect to the parity bit p_(k)from L(u_(k)) and L(p_(k)), respectively. When performing iterativedecoding, L(u*) and L(p*) are sent to a puncture part 306 and convertedto likelihood information L(c*)(the result of combining and thinning outL(u*) and L(p*)). A priori information Le(c) is subtracted from L(c*) bya subtractor 307. Then, interleaving is performed by an interleaver 308on the output of the subtractor 307 so as to obtain La(c_(i)). La(c_(i))is supplied to the a posteriori probability decoder (PR Channel APP) 301as a priori information and iteration is repeatedly performed. Datadetection is performed such that a hard decision part 309 determineswhether L(u*) obtained from the code decoder 305 is “1” or “0” andoutputs the user data sequence U_(k).

[0012] However, the above-described conventional example suffers fromthe following problems.

[0013] Generally, there are local defects in recording media such asoptical disks (including magnetic optical disks), magnetic disks, andmagnetic tapes. Especially, in optical disks and magnetic tapes that arereplaceable media, defective parts are increased by the influence ofadhesion of dust and scratches made when handling them. The iterativedecoding described above operates very effectively for reduced SNRassociated with recording media and apparatuses of higher density. Whena reproduction signal (burst error signal) of a defective part in arecording medium is input, however, likelihood information that is madevastly different via a priori information is propagated to data of apart(s) other than the burst error part, and an error in the burst errorpart is propagated to the data of the other part(s). This is because thelikelihood information obtained from the data of the burst error part isgreatly different from the likelihood information obtained from theoriginal data. Hence, there is a problem in that the effect of errorcorrection by iterative decoding cannot be obtained sufficiently.

SUMMARY OF THE INVENTION

[0014] It is a general object of the present invention to provide animproved and useful data recording/reproducing apparatus and method inwhich the above-mentioned problems are eliminated.

[0015] It is another and more specific object of the present inventionto provide a data recording/reproducing apparatus using iterativedecoding and capable of correctly demodulating data even in a case wherea reproduction signal includes a burst error signal, that is, capable ofadequately obtaining the effect of error correction by iterativedecoding.

[0016] In order to achieve the above-mentioned objects according to oneaspect of the present invention, there is provided arecording/reproducing apparatus that records and reproduces, over apartial response channel, a recording signal produced by encoding dataaccording to a convolutional code and reproduces the data from areproduction signal by iterative decoding using likelihood information,the recording/reproducing apparatus including:

[0017] a burst error detector detecting a burst error part in thereproduction signal; and

[0018] a substituting part substituting, for a sampling value includedin the burst error part, a predetermined value according to a detectedresult of the burst error detector.

[0019] According to the present invention, by detecting a burst errorpart and substituting, for the burst error part, a value that does notexert influence on a part(s) other than the burst error part, it ispossible to control the influence of wrong likelihood information initerative decoding. Thus, it is possible to maintain the decodingability of iterative decoding.

[0020] As described above, according to the present invention, wronglikelihood information is not propagated even if a reproduction signalincludes a burst error part. Hence, it is possible to obtain arecording/reproducing apparatus having high decoding ability even withlow S/N ratios by iterative decoding.

[0021] Other objects, features and advantages of the present inventionwill become more apparent from the following detailed description whenread in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a block diagram showing the construction of aconventional data recording apparatus using iterative decoding;

[0023]FIG. 2 is a block diagram showing an example of the constructionof an encoder that encodes user data to codes for performing iterativedecoding;

[0024]FIG. 3 is a block diagram showing an example of a conventionalconstruction of the iterative decoder shown in FIG. 1;

[0025]FIG. 4 is a block diagram showing a first embodiment of thepresent invention;

[0026]FIG. 5 is a block diagram showing a second embodiment of thepresent invention;

[0027]FIG. 6 is a block diagram showing a third embodiment of thepresent invention;

[0028]FIG. 7 is a block diagram showing a fourth embodiment of thepresent invention;

[0029]FIG. 8 is a block diagram showing a fifth embodiment of thepresent invention;

[0030]FIG. 9 is a block diagram showing a sixth embodiment of thepresent invention

[0031]FIG. 10 is a timing diagram showing an operation example of aburst error waveform;

[0032]FIG. 11 is a block diagram showing a seventh embodiment of thepresent invention;

[0033]FIG. 12 is a graph showing simulation results of the error ratewith respect to the number of times of iteration of iterative decodingusing the present invention;

[0034]FIG. 13 is a block diagram showing one embodiment of a burst errordetector of the present invention; and

[0035]FIG. 14 is a timing diagram for explaining the operation of theburst error detector of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] A description will be given of preferred embodiments of thepresent invention.

[0037]FIG. 4 shows a first embodiment of the present invention. Thefirst embodiment of the present invention shown in FIG. 4 differs fromthe recording/reproducing system of optical disks using conventionaliterative decoding shown in FIG. 1 in that a burst error detector 401 asburst detecting means and a substituting circuit 402 as substitutingmeans are provided in the first embodiment shown in FIG. 4. Fundamentalrecording and reproducing of data in the first embodiment are the sameas those explained with reference to FIG. 1.

[0038] In the first embodiment shown in FIG. 4, the A/D converter 114converts the MO reproduction signal subjected to waveform equalizationinto digital data, and, from this value, the burst error detector 401detects a burst error region from the value. Then, the substitutingcircuit 402 substitutes, for the data corresponding to the burst errorpart, likelihood information that does not affect (that hardlypropagates the error to) data of parts other than the burst error partwhen iterative decoding is performed by the iterative decoder 116. Thedata whose value in the burst error part is substituted for areaccumulated in the memory 115. The data are substituted for withlikelihood information representing that the probability of “1” and theprobability of “0” are the same probabilities. For example, in a casewhere highest likelihood information of probability that data are “1”(lowest likelihood information of probability that data are “0”) is +1,and lowest likelihood information of probability that data are “1”(highest likelihood information of probability that data are “0”) is −1,the data to be substituted for are replaced by the intermediate value“0” of likelihood information. Hence, it is possible to exert the leastinfluence of the burst error part on parts other than the burst errorpart. In this manner, the iterative decoder 116 performs iterativedecoding on the data accumulated in the memory 115, including the datain the burst error part whose values are substituted. It should be notedthat the reason for accumulating data in the memory 115 is that theiterative process of the iterative decoder 116 is an operation having alower rate than the channel transfer rate. Moreover, another reason isthat, in iterative decoding, it is necessary to perform a backwardoperation with respect to pathmetric. In some cases, the memory 115 maynot be required depending on the execution method of the followingiterative decoding.

[0039] Next, FIG. 5 shows a second embodiment of the present invention.In this embodiment, the MO reproduction signal subjected to waveformequalization is converted to a digital signal by the A/D converter 114,and thereafter the digital value is temporarily accumulated in thememory 115. Then, using the accumulated values, a burst error isdetected by the burst error detector 401, and the substitution of datais performed by the substituting circuit 402. The data to be substitutedare the same as those in the first embodiment shown in FIG. 4.

[0040] In this embodiment, while reading the data from the memory 115,the read data are substituted and then supplied to the iterative decoder116. It is possible to replace burst error data in this manner.

[0041]FIG. 6 shows a third embodiment of the present invention. In thisembodiment, while reading the data from the memory 115, a burst error isdetected by the burst error detector 401, the read data are substitutedby the substituting circuit 402, and then the data are written again inthe memory 115. The data to be substituted are the same as those in thefirst embodiment shown in FIG. 4. It is possible to substitute the datain the memory 115 in this manner.

[0042]FIG. 7 shows a fourth embodiment of the present invention. In FIG.7, those parts that are designated by the same reference numerals inFIG. 3 are the same as those corresponding parts in FIG. 3. In thisembodiment, the output of the a posteriori probability decoder (PRChannel APP) 301 is substituted for. In FIG. 7, using the data outputfrom the memory 115, which data are the input to the a posterioriprobability decoder 301, a burst error position is detected by the bursterror detector 401, and the output of the a posteriori probabilitydecoder 301 is replaced by the substituting circuit 701. It is possibleto substitute for burst error data in this manner. The data to bereplaced are substituted for with likelihood information representingthat the probability of “1” and the probability of “0” are the sameprobability. For example, in a case where highest likelihood informationof probability that data are “1” (lowest likelihood information ofprobability that data are “0”) is “+1”, and lowest likelihoodinformation of probability that data are “1” (highest likelihoodinformation of probability that data are “0”) is “−1”, the data arereplaced with the intermediate value “0” of likelihood information.Hence, it is possible to exert the least influence of the burst errorpart on parts other than the burst error part.

[0043] Next, a description will be given of a fifth embodiment of thepresent invention. FIG. 8 shows the fifth embodiment of the presentinvention. In the embodiment shown in FIG. 8, those parts that aredesignated by the same reference numerals in the fourth embodiment shownin FIG. 7 are the same as those corresponding parts in FIG. 7. The fifthembodiment of the present invention shown in FIG. 8 differs from thefourth embodiment of the present invention shown in FIG. 7 in that aselect circuit 801 is provided in the fifth embodiment.

[0044] In the initial stage of iterative decoding, such as the number oftimes of iteration is one and two, likelihood information of the PRchannel corresponding to the burst error part exerts great influence onlikelihood information of parts other than the burst error part. Inorder to control this, in this embodiment, based on control information118 of the number of times of iteration supplied to the iterativedecoder 116 from the controller 117 shown in FIG. 1, whether to selectand send, to the subtractor 302, L(c_(i)*) that is output from the aposteriori probability decoder 301 or to select and send, to thesubtractor 302, the output of the substituting circuit 701 is controlledin accordance with the number of times of iterative decoding.

[0045] Next, a description will be given of a sixth embodiment of thepresent invention. FIG. 9 shows the sixth embodiment of the presentinvention. In this embodiment, data of a burst error part and vicinityare replaced through performing a predetermined operation by anoperation part 901 with respect to the data accumulated in the memory115 and corresponding to the burst error part and vicinity detected bythe burst error detector 401.

[0046]FIG. 10 shows one embodiment of the operation with respect to aburst error waveform. FIG. 10-A represents a reproduction waveform of aburst error part, FIG. 10-B represents an operation coefficient k, andFIG. 10-C represents the waveform after the operation by the operationpart 901. In FIG. 10-A, yt indicates each sampling value, a time periodT indicates the burst error part, B1 indicates a threshold value on thepositive side of a burst error detection level, B2 indicates a thresholdvalue on the negative side of the burst error detection level, and Cindicates the center value. The operation of the operation part 901 isperformed according to:

yt′=k*yt+C(1−k)  (1)

[0047] where yt′ is the sampling value after the operation.

[0048] First, the burst error detector 401 shown in FIG. 9 reads theaccumulated data from the memory 115 and detects the burst error part T.Then, with a central focus on the range of the burst error part, thesampling value is calculated according to the equation (1) by using theoperation coefficient k represented by FIG. 10-B. For example, in FIG.10-A, when the sampling value yt has an amplitude greater than thethreshold value B1 in the time period 25-32, the burst error detector401 detects that a burst error part due to scratches of dust exists.Usually, the influence of such as scratches is exerted also on partsbefore and after the burst error part. Therefore, while reading the datafrom the memory 115, the operation coefficient k is varied as indicatedby FIG. 10-B, including the parts before and after the burst error partT.

[0049] When the operation is executed according to the equation (1) byusing the operation coefficient k, as represented by FIG. 10-C, theamplitude of the signal of the burst error part becomes small andassumes values close to the center value C. In the case where thereproduction waveform of FIG. 10-A is the waveform of PR(1, 1), thecenter value C is a value at which whether data are “1” or “0” cannot bedetermined. Thus, according to the operation of this embodiment, it ispossible to substitute, for the burst error part, likelihood informationof the iterative decoding process that does not exert influence on otherdata.

[0050] As described above, in the embodiments of the present inventionexplained with reference to FIGS. 4 through 10, the values of the bursterror part in the sampling values of the MO reproduction waveformdigitized by the A/D converter 114 are directly replaced or replacedthrough the operation, with values that do not exert influence onlikelihood information of parts other than the burst error part. Thatis, the values of the burst error part are replaced by other values inthe part corresponding to the PR channel data.

[0051] Next, a description will be given of a seventh embodiment of thepresent invention. FIG. 11 shows the seventh embodiment of the presentinvention. In this embodiment, those parts that are designated by thesame reference numerals in FIG. 7 are the same as those correspondingparts in FIG. 7. This embodiment shows an embodiment where datacorresponding to Code data are replaced. In this embodiment, first, aburst error part is detected from the sampling value y_(i) that isoutput from the memory 115. Then, deinterleaving is performed by adeinterleaver 1101 on the position of the detected burst error part, andthe position corresponding to the burst error part on the PR channel isconverted so as to correspond to the output of the deinterleaver 303 andsupplied to a substituting circuit 1102 as substituting means.

[0052] The substituting circuit 1102 substitutes, for likelihoodinformation of the part corresponding to the burst error part, thedeinterleaved extrinsic likelihood information Le(c) output from thedeinterleaver 303. In this case, the likelihood information Le(c) is alikelihood information ratio. Thus, if the probability that data are “1”is 100%, then Le(c)=1, and if the probability that data are “0” is 100%,then Le(c)=−1. In addition, if the probability that data are “1” and theprobability that data are “0” are the same, then Le(c)=0. Accordingly,the likelihood information Le(c) corresponding to the burst error partis substituted as the value 0. In this manner, by substituting thelikelihood information representing that the probability that data are“1” and the probability that data are “0” are same, the influence of theburst error part is not propagated to parts other than the burst errorpart.

[0053] Next, a description will be given of simulation results of theerror rate with respect to the number of times of iteration of theiterative decoding according to the present invention, in a case where aburst error part was generated. FIG. 12 shows the simulation results ofthe error rate with respect to the number of times of iteration ofiterative decoding using the present invention. In a result 1201 of thecase where a burst error part did not exist, the error rate at thebeginning of the iterative decoding starts from 4.0×10 ⁻⁴, and as thenumber of times of iteration increases, the error rate falls. Then, inthe third iteration of decoding, the error rate is stabilized at1.0×10⁻⁵.

[0054] On the other hand, in a result 1202 of the case where data of aburst error part were not replaced, the error rate does not fall inaccordance with the increase of the number of times of iteration. Thisis because wrong likelihood information of the burst error part waspropagated to parts other than the burst error part. Thus, the errorrate fluctuated.

[0055] In a result 1203 of the case where data of the burst error partwere replaced according to the present invention, compared with theresult 1201 of the case where the burst error part did not exist, agreater number of times of iteration is required for convergence. As thenumber of times of iteration of the iterative decoding increases,however, the error rate falls. In the fourth iteration of decoding, theerror rate reaches an equivalent error rate of the result 1201 of thecase where the burst error part did not exist.

[0056] As described above, with the iteration decoding method accordingto the present invention, it is possible to obtain a system that doesnot propagate wrong likelihood information to parts outside of the bursterror part and, by iterative decoding, possesses high decoding abilityeven for low S/N ratios.

[0057] Next, by referring to FIGS. 13 and 14, a description will begiven of one embodiment of the burst error detector of the presentinvention. FIG. 13 shows the embodiment of a burst error detector 1300as burst detecting means of the present invention. FIG. 14 is a timingdiagram for explaining the operation of the burst error detector 1300 ofthe present invention.

[0058]FIG. 13 shows the embodiment of the burst error detector 1300. Theburst error detector 1300 includes comparators 1301 and 1302, shiftregisters 1303 and 1304, and an OR circuit 1305. Each of the comparators1301 and 1302 includes an input a and an input b, and it is assumed thatwhen a is equal to or greater than b, the output is at a high level, andwhen a<b, the output is at a low level. The comparator 1301 compares thesampling value yi with B1 shown in FIG. 10-A, and determines whether thesampling value yi is in a burst error part. The comparator 1302 comparesthe sampling value yi with B2 shown in FIG. 10-A, and determines whetherthe sampling value yi is in a burst error part. The output of the twocomparators 1301 and 1302 are input to the N-stage shift registers 1303and 1304, respectively, which represent a burst error position. Alloutput of each of the shift registers 1303 and 1304 is input to the ORcircuit 1305.

[0059] The output of the OR circuit 1305 is a burst error gate signal(BG), that is, the burst error period T in FIG. 10-A. However, when thesampling value yi is delayed for N/2 stages of the shift register in ashifting circuit such as the shifting circuit 402 shown in FIG. 5, theBG is opened before N/2 of the BP. Thus, it is possible to deal witheven the small influence of a burst error occurring in the hem (tailends) of a Gaussian distribution of an optical beam due to dust andscratches.

[0060]FIG. 14 shows the operation of the burst error detector 1300. FIG.14-A shows the sampling values obtained by sampling a signal 1401 thatdoes not include a burst error part in reproduction data, and thesampling values obtained by sampling a signal 1402 that includes a bursterror part in reproduction data.

[0061] As explained by referring to FIG. 13, the burst error detector1300 determines that yi is at the burst error position BP when yi isgreater than the threshold value B1 on the positive side of the bursterror detection level, or when yi is smaller than the threshold value B2on the negative side of the burst error detection level.

[0062] In this embodiment shown in FIG. 14, the case is shown where thenumber of stages of the shift registers 1303 and 1304 shown in FIG. 13is, for example, N=4. As indicated by FIG. 14-B, when yi is greater thanthe threshold value B1 on the positive side of the burst error detectionlevel, the outputs of the shift register 1303 are high levels 1403through 1406. On the other hand, as indicated by FIG. 14-C, when yi issmaller than the threshold value B2 on the negative side of the bursterror detection level, the outputs of the shift register 1304 are highlevels 1407 and 1408. When all of the outputs of the N stages of each ofthe shift registers 1303 and 1304 are input to the OR circuit 1305, asindicated by FIG. 14-D, a signal comprising high levels 1409 through1411 in the burst error periods is obtained as the output of the ORcircuit 1305. In this manner, it is possible to generate the burst errorgate signal BG having a time period of the intervals under the influenceof the burst error.

[0063] As described above, by supplying the burst error signal generatedby the burst error detector 1300 to a substituting circuit assubstituting means such as the substituting circuit 402 shown in FIG. 5,it is possible to replace the burst error part with a predeterminedsignal or by an operation.

[0064] In addition, FIG. 14-E indicates sampling values 1412 obtained bydelaying, for N/2=2 clocks in the substituting circuit, the signal 1401that does not include the burst error part in the reproduction data, andsampling values 1413 obtained by delaying, for N/2=2 clocks in thesubstituting circuit, the signal 1402 that includes the burst error partin the reproduction data. In this manner, by delaying the sampling valueyi for N/2 stages in the substituting circuit with respect to the bursterror gate signal BG generated by the burst error detector 1300, it isalso possible to substitute the predetermined signal or by an operation,for the sampling value yi under the influence of the burst error part ina part before the burst error position BP.

[0065] As described above, according to the present invention, bydetecting a burst error part and substituting for the burst error part avalue that does not affect parts other than the burst error part, it ispossible to control the influence of wrong likelihood information initerative decoding. Accordingly, it is possible to maintain the decodingability of iterative decoding.

[0066] In addition, according to the present invention, wrong likelihoodinformation is not propagated even if a reproduction signal includes aburst error part. Hence, it is possible to obtain arecording/reproducing apparatus having high decoding ability even withlow S/N ratios by iterative decoding.

[0067] The present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the present invention.

[0068] The present application is based on Japanese priority applicationNo. 2002-246841 filed on Aug. 27, 2002, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A recording/reproducing apparatus that recordsand reproduces, over a partial response channel, a recording signalproduced by encoding data according to a convolutional code andreproduces the data from a reproduction signal by iterative decodingusing likelihood information, said recording/reproducing apparatuscomprising: a burst error detector detecting a burst error part in thereproduction signal; and a substituting part substituting, for asampling value included in the burst error part, a predetermined valueaccording to a detected result of said burst error detector.
 2. Therecording/reproducing apparatus as claimed in claim 1, wherein thepredetermined value is a value by which influence of the sampling valuein the burst error part is not propagated, when performing the iterativedecoding of the data by using likelihood information of a sample in apart other than the burst error part.
 3. The recording/reproducingapparatus as claimed in claim 1, wherein the predetermined value is oneof a sampling value and a likelihood information value with which aprobability that a data value obtained through the iterative decoding is“0” and a probability that a data value obtained through the iterativedecoding is “1” become the same.
 4. The recording/reproducing apparatusas claimed in claim 3, wherein the likelihood information is a valuecorresponding to data output from the partial response channel.
 5. Therecording/reproducing apparatus as claimed in claim 3, wherein thelikelihood information corresponds to data output through decoding ofthe convolutional code.
 6. The recording/reproducing apparatus asclaimed in claim 1, wherein the burst error detector determines that asample is included in the burst error part in one of the case whereinthe sampling value is greater than a first detection level and the casewherein the sampling value is smaller than a second detection level,where the first detection level is higher than the second detectionlevel.
 7. The recording/reproducing apparatus as claimed in claim 1,wherein the substituting part substitutes, after delaying the samplingvalue, the predetermined value for the sampling value according to adetected result of the burst error detector.
 8. Therecording/reproducing apparatus as claimed in claim 1, wherein thesubstituting part controls whether or not to substitute for the samplingvalue in accordance with the number of times of iteration of theiterative decoding.
 9. A recording/reproducing apparatus that recordsand reproduces, over a partial response channel, a recording signalproduced by encoding data according to a convolutional code andreproduces the data from a reproduction signal by iterative decodingusing likelihood information, said recording/reproducing apparatuscomprising: a burst error detector detecting a burst error part in thereproduction signal; and a substituting part substituting for a samplingvalue including the burst error part through a predetermined operation.10. The recording/reproducing apparatus as claimed in claim 9, whereinthe predetermined operation reduces an amplitude of a signal of thesampling value including the burst error part.
 11. Therecording/reproducing apparatus as claimed in claim 9, wherein thesubstituting part substitutes, after delaying the sampling value, forthe sampling value through the predetermined operation according to adetected result of the burst error detector.
 12. A method ofsubstituting for a burst error part in a reproduction signal reproducedby a recording/reproducing apparatus that records and reproduces, over apartial response channel, a recording signal produced by encoding dataaccording to a convolutional code and reproduces the data from thereproduction signal by iterative decoding using likelihood information,said method comprising the steps of: detecting the burst error part inthe reproduction signal; and substituting, for a sampling value includedin the burst error part, a predetermined value according to a detectedresult of the step of detecting the burst error part.
 13. The method asclaimed in claim 12, wherein the predetermined value is a value by whichinfluence of the sampling value in the burst error part is notpropagated, when performing the iterative decoding of the data by usinglikelihood information of a sample in a part other than the burst errorpart.
 14. The method as claimed in claim 12, wherein the predeterminedvalue is one of a sampling value and a likelihood information value withwhich a probability that a data value obtained through the iterativedecoding is “0” and a probability that a data value obtained through theiterative decoding is “1” become the same.